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            <h1>es6-Generator</h1>
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        <a class="nexmoefont icon-calendar-fill">2021年07月15日</a>
        
            <a class="nexmoefont icon-appstore-fill -link" href="/categories/%E5%89%8D%E7%AB%AF/">前端</a>
        
        
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    <p>Generator 函数是 ES6 提供的一种异步编程解决方案，语法行为与传统函数完全不同</p>
<span id="more"></span>
<h2 id="一、介绍"><a href="#一、介绍" class="headerlink" title="一、介绍"></a>一、介绍</h2><p><img onerror="imgOnError(this);" data-fancybox="gallery" src="https://cdn.tangyuxian.com/PicGoImages/20210715155400.webp" alt="图片" data-caption="图片" loading="lazy"></p>
<p>回顾下上文提到的解决异步的手段：</p>
<ul>
<li>回调函数</li>
<li>promise</li>
</ul>
<p>那么，上文我们提到<code>promsie</code>已经是一种比较流行的解决异步方案，那么为什么还出现<code>Generator</code>？甚至<code>async/await</code>呢？</p>
<p>该问题我们留在后面再进行分析，下面先认识下<code>Generator</code></p>
<h3 id="Generator函数"><a href="#Generator函数" class="headerlink" title="Generator函数"></a>Generator函数</h3><p>执行 <code>Generator</code> 函数会返回一个遍历器对象，可以依次遍历 <code>Generator</code> 函数内部的每一个状态</p>
<p>形式上，<code>Generator</code>函数是一个普通函数，但是有两个特征：</p>
<ul>
<li><code>function</code>关键字与函数名之间有一个星号</li>
<li>函数体内部使用<code>yield</code>表达式，定义不同的内部状态</li>
</ul>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* helloWorldGenerator() {</span></span>
<span class="line"><span style="color: #e1e4e8">  yield &#39;hello&#39;;</span></span>
<span class="line"><span style="color: #e1e4e8">  yield &#39;world&#39;;</span></span>
<span class="line"><span style="color: #e1e4e8">  return &#39;ending&#39;;</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span></code></pre></div></div></figure>

<h2 id="二、使用"><a href="#二、使用" class="headerlink" title="二、使用"></a>二、使用</h2><p><code>Generator</code> 函数会返回一个遍历器对象，即具有<code>Symbol.iterator</code>属性，并且返回给自己</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* gen(){</span></span>
<span class="line"><span style="color: #e1e4e8">  // some code</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">var g = gen();</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">g[Symbol.iterator]() === g</span></span>
<span class="line"><span style="color: #e1e4e8">// true</span></span></code></pre></div></div></figure>

<p>通过<code>yield</code>关键字可以暂停<code>generator</code>函数返回的遍历器对象的状态</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* helloWorldGenerator() {</span></span>
<span class="line"><span style="color: #e1e4e8">  yield &#39;hello&#39;;</span></span>
<span class="line"><span style="color: #e1e4e8">  yield &#39;world&#39;;</span></span>
<span class="line"><span style="color: #e1e4e8">  return &#39;ending&#39;;</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8">var hw = helloWorldGenerator();</span></span></code></pre></div></div></figure>

<p>上述存在三个状态：<code>hello</code>、<code>world</code>、<code>return</code></p>
<p>通过<code>next</code>方法才会遍历到下一个内部状态，其运行逻辑如下：</p>
<ul>
<li>遇到<code>yield</code>表达式，就暂停执行后面的操作，并将紧跟在<code>yield</code>后面的那个表达式的值，作为返回的对象的<code>value</code>属性值。</li>
<li>下一次调用<code>next</code>方法时，再继续往下执行，直到遇到下一个<code>yield</code>表达式</li>
<li>如果没有再遇到新的<code>yield</code>表达式，就一直运行到函数结束，直到<code>return</code>语句为止，并将<code>return</code>语句后面的表达式的值，作为返回的对象的<code>value</code>属性值。</li>
<li>如果该函数没有<code>return</code>语句，则返回的对象的<code>value</code>属性值为<code>undefined</code></li>
</ul>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">hw.next()</span></span>
<span class="line"><span style="color: #e1e4e8">// { value: &#39;hello&#39;, done: false }</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">hw.next()</span></span>
<span class="line"><span style="color: #e1e4e8">// { value: &#39;world&#39;, done: false }</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">hw.next()</span></span>
<span class="line"><span style="color: #e1e4e8">// { value: &#39;ending&#39;, done: true }</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">hw.next()</span></span>
<span class="line"><span style="color: #e1e4e8">// { value: undefined, done: true }</span></span></code></pre></div></div></figure>

<p><code>done</code>用来判断是否存在下个状态，<code>value</code>对应状态值</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">yield`表达式本身没有返回值，或者说总是返回`undefined</span></span></code></pre></div></div></figure>

<p>通过调用<code>next</code>方法可以带一个参数，该参数就会被当作上一个<code>yield</code>表达式的返回值</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* foo(x) {</span></span>
<span class="line"><span style="color: #e1e4e8">  var y = 2 * (yield (x + 1));</span></span>
<span class="line"><span style="color: #e1e4e8">  var z = yield (y / 3);</span></span>
<span class="line"><span style="color: #e1e4e8">  return (x + y + z);</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">var a = foo(5);</span></span>
<span class="line"><span style="color: #e1e4e8">a.next() // Object{value:6, done:false}</span></span>
<span class="line"><span style="color: #e1e4e8">a.next() // Object{value:NaN, done:false}</span></span>
<span class="line"><span style="color: #e1e4e8">a.next() // Object{value:NaN, done:true}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">var b = foo(5);</span></span>
<span class="line"><span style="color: #e1e4e8">b.next() // { value:6, done:false }</span></span>
<span class="line"><span style="color: #e1e4e8">b.next(12) // { value:8, done:false }</span></span>
<span class="line"><span style="color: #e1e4e8">b.next(13) // { value:42, done:true }</span></span></code></pre></div></div></figure>

<p>正因为<code>Generator</code>函数返回<code>Iterator</code>对象，因此我们还可以通过<code>for...of</code>进行遍历</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* foo() {</span></span>
<span class="line"><span style="color: #e1e4e8">  yield 1;</span></span>
<span class="line"><span style="color: #e1e4e8">  yield 2;</span></span>
<span class="line"><span style="color: #e1e4e8">  yield 3;</span></span>
<span class="line"><span style="color: #e1e4e8">  yield 4;</span></span>
<span class="line"><span style="color: #e1e4e8">  yield 5;</span></span>
<span class="line"><span style="color: #e1e4e8">  return 6;</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">for (let v of foo()) {</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(v);</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8">// 1 2 3 4 5</span></span></code></pre></div></div></figure>

<p>原生对象没有遍历接口，通过<code>Generator</code>函数为它加上这个接口，就能使用<code>for...of</code>进行遍历了</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* objectEntries(obj) {</span></span>
<span class="line"><span style="color: #e1e4e8">  let propKeys = Reflect.ownKeys(obj);</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">  for (let propKey of propKeys) {</span></span>
<span class="line"><span style="color: #e1e4e8">    yield [propKey, obj[propKey]];</span></span>
<span class="line"><span style="color: #e1e4e8">  }</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">let jane = { first: &#39;Jane&#39;, last: &#39;Doe&#39; };</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">for (let [key, value] of objectEntries(jane)) {</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(`${key}: ${value}`);</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8">// first: Jane</span></span>
<span class="line"><span style="color: #e1e4e8">// last: Doe</span></span></code></pre></div></div></figure>

<h2 id="三、异步解决方案"><a href="#三、异步解决方案" class="headerlink" title="三、异步解决方案"></a>三、异步解决方案</h2><p>回顾之前展开异步解决的方案：</p>
<ul>
<li>回调函数</li>
<li>Promise 对象</li>
<li>generator 函数</li>
<li>async&#x2F;await</li>
</ul>
<p>这里通过文件读取案例，将几种解决异步的方案进行一个比较：</p>
<h3 id="回调函数"><a href="#回调函数" class="headerlink" title="回调函数"></a>回调函数</h3><p>所谓回调函数，就是把任务的第二段单独写在一个函数里面，等到重新执行这个任务的时候，再调用这个函数</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">fs.readFile(&#39;/etc/fstab&#39;, function (err, data) {</span></span>
<span class="line"><span style="color: #e1e4e8">  if (err) throw err;</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(data);</span></span>
<span class="line"><span style="color: #e1e4e8">  fs.readFile(&#39;/etc/shells&#39;, function (err, data) {</span></span>
<span class="line"><span style="color: #e1e4e8">    if (err) throw err;</span></span>
<span class="line"><span style="color: #e1e4e8">    console.log(data);</span></span>
<span class="line"><span style="color: #e1e4e8">  });</span></span>
<span class="line"><span style="color: #e1e4e8">});</span></span></code></pre></div></div></figure>

<p><code>readFile</code>函数的第三个参数，就是回调函数，等到操作系统返回了<code>/etc/passwd</code>这个文件以后，回调函数才会执行</p>
<h3 id="Promise"><a href="#Promise" class="headerlink" title="Promise"></a>Promise</h3><p><code>Promise</code>就是为了解决回调地狱而产生的，将回调函数的嵌套，改成链式调用</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">const fs = require(&#39;fs&#39;);</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">const readFile = function (fileName) {</span></span>
<span class="line"><span style="color: #e1e4e8">  return new Promise(function (resolve, reject) {</span></span>
<span class="line"><span style="color: #e1e4e8">    fs.readFile(fileName, function(error, data) {</span></span>
<span class="line"><span style="color: #e1e4e8">      if (error) return reject(error);</span></span>
<span class="line"><span style="color: #e1e4e8">      resolve(data);</span></span>
<span class="line"><span style="color: #e1e4e8">    });</span></span>
<span class="line"><span style="color: #e1e4e8">  });</span></span>
<span class="line"><span style="color: #e1e4e8">};</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">readFile(&#39;/etc/fstab&#39;).then(data =&gt;{</span></span>
<span class="line"><span style="color: #e1e4e8">    console.log(data)</span></span>
<span class="line"><span style="color: #e1e4e8">    return readFile(&#39;/etc/shells&#39;)</span></span>
<span class="line"><span style="color: #e1e4e8">}).then(data =&gt; {</span></span>
<span class="line"><span style="color: #e1e4e8">    console.log(data)</span></span>
<span class="line"><span style="color: #e1e4e8">})</span></span></code></pre></div></div></figure>

<p>这种链式操作形式，使异步任务的两段执行更清楚了，但是也存在了很明显的问题，代码变得冗杂了，语义化并不强</p>
<h3 id="generator"><a href="#generator" class="headerlink" title="generator"></a>generator</h3><p><code>yield</code>表达式可以暂停函数执行，<code>next</code>方法用于恢复函数执行，这使得<code>Generator</code>函数非常适合将异步任务同步化</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">const gen = function* () {</span></span>
<span class="line"><span style="color: #e1e4e8">  const f1 = yield readFile(&#39;/etc/fstab&#39;);</span></span>
<span class="line"><span style="color: #e1e4e8">  const f2 = yield readFile(&#39;/etc/shells&#39;);</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(f1.toString());</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(f2.toString());</span></span>
<span class="line"><span style="color: #e1e4e8">};</span></span></code></pre></div></div></figure>

<h3 id="async-await"><a href="#async-await" class="headerlink" title="async&#x2F;await"></a>async&#x2F;await</h3><p>将上面<code>Generator</code>函数改成<code>async/await</code>形式，更为简洁，语义化更强了</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">const asyncReadFile = async function () {</span></span>
<span class="line"><span style="color: #e1e4e8">  const f1 = await readFile(&#39;/etc/fstab&#39;);</span></span>
<span class="line"><span style="color: #e1e4e8">  const f2 = await readFile(&#39;/etc/shells&#39;);</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(f1.toString());</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(f2.toString());</span></span>
<span class="line"><span style="color: #e1e4e8">};</span></span></code></pre></div></div></figure>

<h3 id="区别："><a href="#区别：" class="headerlink" title="区别："></a>区别：</h3><p>通过上述代码进行分析，将<code>promise</code>、<code>Generator</code>、<code>async/await</code>进行比较：</p>
<ul>
<li><code>promise</code>和<code>async/await</code>是专门用于处理异步操作的</li>
<li><code>Generator</code>并不是为异步而设计出来的，它还有其他功能（对象迭代、控制输出、部署<code>Interator</code>接口…）</li>
<li><code>promise</code>编写代码相比<code>Generator</code>、<code>async</code>更为复杂化，且可读性也稍差</li>
<li><code>Generator</code>、<code>async</code>需要与<code>promise</code>对象搭配处理异步情况</li>
<li><code>async</code>实质是<code>Generator</code>的语法糖，相当于会自动执行<code>Generator</code>函数</li>
<li><code>async</code>使用上更为简洁，将异步代码以同步的形式进行编写，是处理异步编程的最终方案</li>
</ul>
<h2 id="四、使用场景"><a href="#四、使用场景" class="headerlink" title="四、使用场景"></a>四、使用场景</h2><p><code>Generator</code>是异步解决的一种方案，最大特点则是将异步操作同步化表达出来</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* loadUI() {</span></span>
<span class="line"><span style="color: #e1e4e8">  showLoadingScreen();</span></span>
<span class="line"><span style="color: #e1e4e8">  yield loadUIDataAsynchronously();</span></span>
<span class="line"><span style="color: #e1e4e8">  hideLoadingScreen();</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8">var loader = loadUI();</span></span>
<span class="line"><span style="color: #e1e4e8">// 加载UI</span></span>
<span class="line"><span style="color: #e1e4e8">loader.next()</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">// 卸载UI</span></span>
<span class="line"><span style="color: #e1e4e8">loader.next()</span></span></code></pre></div></div></figure>

<p>包括<code>redux-saga</code>中间件也充分利用了<code>Generator</code>特性</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">import { call, put, takeEvery, takeLatest } from &#39;redux-saga/effects&#39;</span></span>
<span class="line"><span style="color: #e1e4e8">import Api from &#39;...&#39;</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">function* fetchUser(action) {</span></span>
<span class="line"><span style="color: #e1e4e8">   try {</span></span>
<span class="line"><span style="color: #e1e4e8">      const user = yield call(Api.fetchUser, action.payload.userId);</span></span>
<span class="line"><span style="color: #e1e4e8">      yield put({type: &quot;USER_FETCH_SUCCEEDED&quot;, user: user});</span></span>
<span class="line"><span style="color: #e1e4e8">   } catch (e) {</span></span>
<span class="line"><span style="color: #e1e4e8">      yield put({type: &quot;USER_FETCH_FAILED&quot;, message: e.message});</span></span>
<span class="line"><span style="color: #e1e4e8">   }</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">function* mySaga() {</span></span>
<span class="line"><span style="color: #e1e4e8">  yield takeEvery(&quot;USER_FETCH_REQUESTED&quot;, fetchUser);</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">function* mySaga() {</span></span>
<span class="line"><span style="color: #e1e4e8">  yield takeLatest(&quot;USER_FETCH_REQUESTED&quot;, fetchUser);</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">export default mySaga;</span></span></code></pre></div></div></figure>

<p>还能利用<code>Generator</code>函数，在对象上实现<code>Iterator</code>接口</p>
<figure class="shiki"><div class='codeblock'><div class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></div><div class="code"><pre class="shiki github-dark"><code><span class="line"><span style="color: #e1e4e8">function* iterEntries(obj) {</span></span>
<span class="line"><span style="color: #e1e4e8">  let keys = Object.keys(obj);</span></span>
<span class="line"><span style="color: #e1e4e8">  for (let i=0; i &lt; keys.length; i++) {</span></span>
<span class="line"><span style="color: #e1e4e8">    let key = keys[i];</span></span>
<span class="line"><span style="color: #e1e4e8">    yield [key, obj[key]];</span></span>
<span class="line"><span style="color: #e1e4e8">  }</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">let myObj = { foo: 3, bar: 7 };</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">for (let [key, value] of iterEntries(myObj)) {</span></span>
<span class="line"><span style="color: #e1e4e8">  console.log(key, value);</span></span>
<span class="line"><span style="color: #e1e4e8">}</span></span>
<span class="line"><span style="color: #e1e4e8"></span></span>
<span class="line"><span style="color: #e1e4e8">// foo 3</span></span>
<span class="line"><span style="color: #e1e4e8">// bar 7</span></span></code></pre></div></div></figure>

<hr>
<p>文章来源:<a target="_blank" rel="noopener" href="https://mp.weixin.qq.com/s?__biz=MzU1OTgxNDQ1Nw==&mid=2247485195&idx=1&sn=f0c7f093abb606c01232c80e1ad0c89e&chksm=fc10c55dcb674c4bb6dbb864233c0dad43b4fb09dfc54775978319888ae3f6ff5454aeba7e1a&scene=21#wechat_redirect">微信公众号文章:怎么理解ES6中 Generator的？使用场景？</a></p>

    
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        width: 2%;
        height: 8%;
        transform: translate(-50%, -50%) rotate(240deg) translateY(-520%);
    }

    .memory:nth-child(42) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(246deg) translateY(-1461%);
    }

    .memory:nth-child(43) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(252deg) translateY(-1461%);
    }

    .memory:nth-child(44) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(258deg) translateY(-1461%);
    }

    .memory:nth-child(45) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(264deg) translateY(-1461%);
    }

    .memory:nth-child(46) {
        background-color: var(--color-primary);
        width: 2%;
        height: 8%;
        transform: translate(-50%, -50%) rotate(270deg) translateY(-520%);
    }

    .memory:nth-child(47) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(276deg) translateY(-1461%);
    }

    .memory:nth-child(48) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(282deg) translateY(-1461%);
    }

    .memory:nth-child(49) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(288deg) translateY(-1461%);
    }

    .memory:nth-child(50) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(294deg) translateY(-1461%);
    }

    .memory:nth-child(51) {
        background-color: var(--color-primary);
        width: 2%;
        height: 8%;
        transform: translate(-50%, -50%) rotate(300deg) translateY(-520%);
    }

    .memory:nth-child(52) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(306deg) translateY(-1461%);
    }

    .memory:nth-child(53) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(312deg) translateY(-1461%);
    }

    .memory:nth-child(54) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(318deg) translateY(-1461%);
    }

    .memory:nth-child(55) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(324deg) translateY(-1461%);
    }

    .memory:nth-child(56) {
        background-color: var(--color-primary);
        width: 2%;
        height: 8%;
        transform: translate(-50%, -50%) rotate(330deg) translateY(-520%);
    }

    .memory:nth-child(57) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(336deg) translateY(-1461%);
    }

    .memory:nth-child(58) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(342deg) translateY(-1461%);
    }

    .memory:nth-child(59) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(348deg) translateY(-1461%);
    }

    .memory:nth-child(60) {
        background-color: #949494;
        width: 1%;
        height: 3%;
        transform: translate(-50%, -50%) rotate(354deg) translateY(-1461%);
    }

    .needle {
        position: absolute;
        top: 50%;
        left: 50%;
        transform-origin: center;
    }

    .needle#hours {
        background-color: #1f1f1f;
        width: 4%;
        height: 30%;
        transform-origin: center 75%;
        transform: translate(-50%, -75%);
    }

    .needle#hours.moving {
        transition: transform 150ms ease-out;
    }

    .needle#hours:after {
        content: '';
        background-color: #1f1f1f;
        width: 4vw;
        height: 4vw;
        max-width: 4vh;
        max-height: 4vh;
        display: block;
        position: absolute;
        top: 75%;
        left: 50%;
        box-sizing: border-box;
        border-radius: 50%;
        transform: translate(-50%, -50%);
    }

    .needle#minutes {
        background-color: #1f1f1f;
        width: 2%;
        height: 45%;
        transform-origin: center 75%;
        transform: translate(-50%, -75%);
    }

    .needle#minutes.moving {
        transition: transform 150ms ease-out;
    }

    .needle#minutes:after {
        content: '';
        background-color: #1f1f1f;
        width: 4vw;
        height: 4vw;
        max-width: 4vh;
        max-height: 4vh;
        display: block;
        position: absolute;
        top: 75%;
        left: 50%;
        box-sizing: border-box;
        border-radius: 50%;
        transform: translate(-50%, -50%);
    }

    .needle#seconds {
        background-color: #cb2f2f;
        width: 1%;
        height: 50%;
        transform-origin: center 75%;
        transform: translate(-50%, -75%);
    }

    .needle#seconds.moving {
        transition: transform 150ms ease-out;
    }

    .needle#seconds:after {
        content: '';
        background-color: #cb2f2f;
        width: 2.5vw;
        height: 2.5vw;
        max-width: 2.5vh;
        max-height: 2.5vh;
        display: block;
        position: absolute;
        top: 75%;
        left: 50%;
        box-sizing: border-box;
        border-radius: 50%;
        transform: translate(-50%, -50%);
    }
    .clock_logo{
        width: 10vw;
        height: 10vw;
        max-width: 10vh;
        max-height: 10vh;
        position: absolute;
        top: 50%;
        left: 50%;
        box-sizing: border-box;
        border-radius: 50%;
        transform: translate(-50%, -50%);
        background-size: 100% 100%;
        background-repeat: no-repeat;
    }
    .clock_logo{
            width: 10vw;
            height: 10vw;
            max-width: 10vh;
            max-height: 10vh;
            position: absolute;
            top: 50%;
            left: 50%;
            box-sizing: border-box;
            border-radius: 50%;
            transform: translate(-50%, -50%);
            background-image: var(--clock-logo);
            background-size: 100% 100%;
            background-repeat: no-repeat;
    }
    @media (min-width: 100vh) {
        .clock {
            border: solid 2.8vh var(--color-primary);
            box-shadow: 0 1.4vh 2.8vh var(--color2);
        }
    }

</style>





            </div>
        
            <div class="nexmoe-pd-item">
                <div class="qweather" >
    <div id="he-plugin-standard">
        <iframe allowtransparency="true" frameborder="0" width="304" height="96" scrolling="no" src="//tianqi.2345.com/plugin/widget/index.htm?s=2&z=1&t=0&v=0&d=2&bd=0&k=000000&f=ff8040&ltf=009944&htf=cc0000&q=1&e=1&a=1&c=54511&w=300&h=96&align=center"></iframe>
    </div>
    <div class="qweather-logo">

    </div>
</div>
<style>
    .qweather{
        position: relative;
        padding-right: 5px;
    }
    .qweather #he-plugin-standard {
        border: 2px solid var(--color-primary);
        box-shadow: 0 1px 0 0 var(--color-primary), 0 1px 2px 0 var(--color-primary);
        border-radius: 8px;
        width: 300px;
        overflow: hidden;
    }
    .qweather-logo{
        position: absolute;
        right: 0;
        top: -15px;
        width: 40px;
        height: 40px;
        background-image: var(--qweather-logo);
        background-size: 100% 100%;
        background-repeat: no-repeat;
    }
</style>

            </div>
        
    
</div>
<style>
    .nexmoe-pd {
        left: auto;
        top: 40px;
        right: 0;
    }
    .nexmoe-pd-item{
       display: flex;
        justify-content: center;
        margin-bottom: 30px;
    }
    #nexmoe-pendant .mdui-drawer{
        width: 305px;
    }
    @media screen and (max-width: 1600px) {
        #nexmoe-pendant {
            display: none
        }
    }
</style>
</div><div id="nexmoe-footer"><!--!--></div><div id="nexmoe-search-space"><div class="search-container"><div class="search-header"><div class="search-input-container"><input class="search-input" type="text" placeholder="搜索" onInput="sinput();"></div><a class="search-close" onclick="sclose();">×</a></div><div class="search-body"></div></div></div><div></div><!-- hexo injector body_end start -->
<script src="https://cdn.jsdelivr.net/npm/hexo-shiki-plugin@latest/lib/codeblock.js"></script>

  <script>
  const CODE_CONFIG = {
    beautify: true,
    highlightCopy: true,
    highlightLang: true,
    highlightHeightLimit: null,
    isHighlightShrink: false,
    copy: {
      success: 'Copy Success',
      error: 'Copy Error',
      noSupport: 'Browser Not Support',
    }
  };
  console.log(
    `%c hexo-shiki-plugin %c v1.0.27 %c https://github.com/nova1751/hexo-shiki-plugin`,
    "color: #fff; background: #5f5f5f",
    "color: #fff; background: #80c8f8",
    ""
  );
  </script>
  <!-- hexo injector body_end end --><script src="/live2dw/lib/L2Dwidget.min.js?094cbace49a39548bed64abff5988b05"></script><script>L2Dwidget.init({"model":{"jsonPath":"/live2dw/assets/xiaomai.model.json"},"display":{"position":"left","width":200,"height":500},"mobile":{"show":false},"react":{"opacity":0.9},"log":false,"pluginJsPath":"lib/","pluginModelPath":"assets/","pluginRootPath":"live2dw/","tagMode":false});</script></body></html>